1. Field of the Invention
The present invention relates to ceramic capacitors and more particularly to ceramic feed-through capacitors wherein a pair of discoidal capacitors are arranged in series relationship and such that in the event that one of the discoidal capacitors fails, a second discoidal capacitor will be effective.
2. Description of the Prior Art
Ceramic feed-through capacitors are intended primarily to pass relatively low frequency electrical currents via a lead or conductor through an opening in a conducting wall, screen or the like while presenting a low impedance shunt path to the conducting wall for currents of very and ultra high frequencies. Capacitors of this type known in the art are shown, for example, by U.S. Pat. Nos. 3,243,671 issued Mar. 29, 1966 to Heron et al; 2,756,375, issued July 24, 1956 to Peck; and 3,617,830, issued Nov. 2, 1971 to Perna.
Ceramic feed-through capacitors are commonly used in electronic systems which cannot be easily serviced in applications such as missiles, satellites and space probes, for example. In the event such ceramic capacitors fail, failure is usually the result of shorting across the electrodes within the capacitor thereby causing shorting through the capacitor and consequent loss of the circuit employing the feed-through capacitor.
The possibility for capacitor failure can be reduced by extensive screening and testing of the capacitors before they are employed in a circuit, but it will be readily appreciated that such testing cannot completely preclude the potential of failure of the capacitor during its life. Furthermore, such testing is labor intensive, time consuming and costly.
In addition to, or as an alternative to, such preliminary screening, feed-through capacitors can be employed in series with a fuse device whereby failure of the capacitor by shorting will cause the fuse to function. Fusible capacitors of this type have been considered an improvement since an operational system, even though degraded by high frequency noise, in generally better than shorting and consequent failure of the entire circuit employing the capacitor.
Capacitors of types other than feed-through capacitors, for example, leaded capacitors, have been employed in series to provide a redundant device and to improve reliability. However, no means has been suggested in the prior art to facilitate connection of capacitors in series to form a feed-through capacitor while maintaining the high shielding integrity required of a feed-through capacitor.
Another inherent problem with feed-through capacitors is the occurrence of characteristic resonant dips in the insertion loss of such capacitors at specified frequency ranges, i.e., at specified resonant frequencies the insertion loss characteristic of the capacitor substantially decreases to ranges below desired values. And even though ceramic monolithic capacitors have decided advantages when compared to other types of capacitors in that the resonant dips in the insertion loss occur at relatively high frequencies and the amplitude of the dip is limited; even monolithic capacitors do not yield the results of a theoretically ideal capacitor.